Base plate with toothed hub for press-in attachment of suspension assembly in hard disk drive

ABSTRACT

A base plate for press fitting into an actuator arm boss hole of a predetermined nominal diameter. The base plate has a flange and a hub extending from a region at which the hub meets the flange to an outer end of the hub. The hub has a number of vertical teeth protruding from the hub extending from the outer end of the hub to the region at which the hub meets the flange. The hub has an outer diameter which is greater than the predetermined nominal diameter of the actuator arm boss hole. A corner relief is provided that circumscribes the region at which the hub meets the flange.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/002,068filed Jan. 7, 1998, now abandoned, and is related to application Ser.No. 09/003,872 filed Jan. 7, 1998, now U.S. Pat. No. 6,141,868, onbehalf of Ryan Schmidt, et al. entitled “Method And Apparatus ForPress-In Attachment Of Suspension Assembly In Hard Disk Drive” andassigned to the same assignee as the present invention, which copendingapplication is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to disk head assemblies for supporting read/writeheads adjacent rotating disks in disk drives and more particularly, to abase plate for attaching a head suspension assembly to a head actuatorarm.

2. Description of the Prior Art

In hard disk drives data are stored on magnetizable surfaces of aplurality of rotatable disks that are mounted in a coaxial stack on ahousing of the drive. Transducer heads that write data to and read datafrom the disk surfaces are supported by an actuator that is mounted onthe housing and can be actuated to position the transducer heads inalignment with concentric data tracks defined on the disks. Eachtransducer head is attached to one end of a head suspension that isconnected to an actuator arm that extends from the actuator body. Thesuspensions include a flexible load beam constructed of light sheetsteel that has a bend formed in it. The load beam acts as a spring thatforces the head against the disk surface with an accurate pre-load or“gram Load”. Air turbulence caused by the rotating disks lifts the headsslightly off of the disks so that the heads fly on an air bearing acrossthe disk surfaces. The air bearing force is counteracted by thesuspension gram load.

A head-carrying suspension is attached to an actuator arm using a baseplate that forms a part of the head suspension. The base plate includesa flat flange portion and a cylindrical hub portion or boss. The baseplate hub is passed through a load beam clearance hole and the flange isspot welded to the load beam. The combined base plate, load beam and aflexure make up a head suspension, and the suspension has the hub of thebase plate extending through and beyond the load beam clearance hole.

The hubs of two suspensions are inserted into an actuator arm boss holeformed through an actuator arm extending from an actuator body, one hubentering an actuator arm boss hole from each end of the hole. In theprior art, a swage ball is passed through the cylindrical hubs to forcethe peripheries of the hubs to expand (swage) into tight engagement withthe inner peripheries of the actuator arm boss hole. Thus, an actuatorarm may carry two suspensions on opposite sides thereof to support twotransducer heads in opposing directions, one up and one down.

Problems with this method of mounting transducer heads have arisen asthe need for increased data storage capacity in hard disk drives hasgrown and the size of the disk drive has decreased to fit in small laptop computers. The problem of forming a strong connection between theactuator arms and the transducer suspensions has been made moredifficult as the thickness of the components has become smaller.

Because of the joining of two transducer suspensions to an actuator armby passing a swage ball through two hubs in the same hole in theactuator arm, an asymmetry exists in the forces that are exerted on thehubs to make the joints. Because the transducer heads face in oppositedirections, the hubs on their respective load beams also extend inopposite directions with respect to the direction of passage of the ballthrough the inner diameters of the hubs. For one transducer suspension,the ball is passed in a direction that tends to place the hub incompressive stress while, for the other transducer suspension, thedirection of passage of the ball is such as to tend to place the hub intensile stress. In order to achieve a permanent bond between the hub andthe actuator, the passage of the ball must cause permanent, or plastic,deformation of the hub. This deformation often causes a change in shapeof the flange portion of the base plate, which results in a change inthe suspension gram load. The differences in shape changes and stressesbetween the suspensions swaged in tension and compression causesdifferences in gram load change and hub/actuator joint integrity betweenthese up and down facing parts.

It is therefore an object of this invention to provide a base plate thateliminates the need for swaging and the resulting up and down facinghead pre-load and joint integrity differences.

It is also an object of this invention is to provide a base plate thatcan be is pressed into an a actuator arm to create a press fit.

SUMMARY OF THE INVENTION

Briefly, the invention is concerned with a base plate for press fittinginto an actuator arm boss hole of a predetermined nominal diameter. Thebase plate comprises a flange and a hub extending from a region at whichthe hub meets the flange to an outer end of the hub. The hub has anumber of teeth protruding radially outwardly from the hub and extendingaxially along the hub from the outer end of the hub part way or all theway to the region at which the hub meets the flange.

In accordance with an aspect of the invention, the hub has an outerdiameter at the teeth which is greater than the predetermined nominaldiameter of the actuator arm boss hole.

The unique base plate geometry reduces tooling and press-in forces,provides a more consistent mating between suspension and actuator, andreduces retention torque sensitivity to actuator hole size variation.

The invention utilizes modified post processing that leaves the baseplate with a much higher yield strength than conventionally processedswagable base plates. This increased strength further reduces gram loadchange caused by the attachment process, increases retention torque,reduces burr formation during press-in, and improves suspension handlingdamage resistance.

An advantage of this invention is that it allows the use of a base plateto connect a head suspension to an actuator arm without swaging.

The invention has the advantage that press-in base plates reduce thelarge a stresses and deformations associated with swaging that result ingram load change.

The invention has the further advantage that high integrity joints canbe formed between the actuator and head suspension assemblies, even withlow hub height base plates.

The invention has the further advantage that press-in base plateseliminate the gram load change difference that occurs between up anddown heads resulting from the different mechanics of conventionaltension and compression swaging.

The invention has the further advantage that increased flange yieldstrength results, further reducing gram load change and handling damagesensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to thedrawings in which:

FIG. 1a is top view of a base plate of the prior art;

FIG. 1b is side elevation view of a base plate of FIG. 1a;

FIG. 2 is a perspective view of the base plate of the present invention;

FIG. 3a is top view of a base plate of FIG. 2; and,

FIG. 3b is side elevation view of a base plate of FIG. 3a welded to aload beam and attached to an actuator arm.

In these figures, similar numerals refer to similar elements in thedrawing. It should be understood that the sizes of the differentcomponents in the figures may not be to scale, or in exact proportion,and are shown for visual clarity and for the purpose of explanation.

DETAILED DESCRIPTION OF THE INVENTION

Refer to FIGS. 1a and 1 b which illustrate a base plate of the priorart. An actuator arm and head suspension, which are elements of anactuator arm assembly, are connected end to end by the base plate. Thebase plate includes a flat flange portion 10 and a cylindrical hubportion or boss 12. A base plate typically has an inner barrel shapewith a counter bore 11, a lead-in chamfer 13 and an inner diameter 15.The counter bore and inner diameter are perpendicular to the plane ofthe base plate flange 10. In assembling the suspension, the hub 12 isinserted through a load beam boss hole in a load beam 14 which is partof the suspension and the flange portion 10 is welded 16, 17, to theload beam. The hub is then inserted through an actuator arm boss hole inthe actuator arm 18. A swage ball tool is passed through the centerinner barrel 19 of the hub 12 causing pressure to be applied to causethe hub 12 to expand into the boss hole in the actuator arm, rigidlyconnecting the hub and attached load beam to the actuator arm boss hole.

A stack of head suspensions are assembled to actuator arms by swaging.Transducer heads are attached to the ends of suspensions. Eachsuspension is connected to an actuator arm 18 that extends from anactuator body. Each suspension includes a flexible load beam 14constructed of light sheet steel that will flex sufficiently to permitair turbulence caused by rotating disks, to lift the heads slightly offof the disks so that the heads fly across the disk surfaces on an airbearing. A base plate hub 12 of a base plate 10 is passed through a loadbeam clearance hole and the flange is spot welded 16, 17, etc. to theload beam. The combined base plate and load beam is called a headsuspension, and each head suspension has the hub of a base plateextending through and beyond the load beam clearance hole. Thecylindrical hubs of the two suspensions are inserted into an actuatorarm boss hole formed through the actuator arm, one hub entering theactuator arm boss hole from each end of the hole.

A swage ball is passed through the barrels of all of the cylindricalhubs, loading opposing hubs in tension and compression, to force theperipheries of the hubs to expand (swage) into tight engagement with theinner peripheries of the corresponding actuator arm boss holes. Forexample, one actuator arm may carry two suspensions, on opposite sidesthereof to support two transducer heads, in opposing directions in closeproximity with the surfaces of the two disks in the assembled hard diskdrive.

Because of the joining of two transducer suspensions to an actuator armby passing a swage ball through two hubs in the same hole in theactuator arm, an asymmetry exists in the forces that are exerted on thehubs to make the joints. Because the transducer heads face in oppositedirections, the hubs on their respective load beams also extend inopposite directions with respect to the direction of passage of the ballthrough the inner diameters of the hubs. For one transducer suspension,the ball is passed in a direction that tends to place the hub incompressive stress while, for the other transducer suspension, thedirection of passage of the ball is such as to tend to place the hub intensile stress. In order to achieve a permanent bond between the hub andthe actuator, the passage of the ball must cause permanent, or plastic,deformation of the hub. This deformation often causes a change in shapeof the flange portion of the base plate, which results in a change inthe suspension gram load. The differences in shape changes and stressesbetween the suspensions swaged in tension and compression causesdifferences in gram load change and hub/actuator joint integrity betweenthese up and down facing parts.

Base plates constructed in accordance with the teachings of the presentinvention solve this problem by eliminating the need for swaging. Thebase plates are press fitted into the actuator arm boss holes. A methodand apparatus for doing this during manufacture is described in theabove identified copending application Ser. No. 09/003,872.

Refer to FIG. 2 which is a partially cut away drawing that illustrates abase plate of the present invention. The base plate includes a flatflange portion 200 and a is cylindrical hub portion or boss 202. The hubhas an outer surface and an inner barrel with an inner diameter 204. Theinner diameter is perpendicular to the plane of the base plate flange200. The hub extends from a region 206 at which the hub meets the flangeto an outer end 208 of the hub. The hub has a number of teeth 210, 212,214, 216, 218, 220, 222, 224, 226, 228, protruding radially outwardlyfrom the hub and extending axially along the hub from the end 208 partway or all the way to the region 206 at which the hub meets the flange200. The hub has an outer diameter (including the teeth) which isgreater than a predetermined nominal diameter of an actuator arm bosshole. The outer diameter is shown by broken lines in FIG. 3a. A cornerrelief groove 225 may be provided that circumscribes the region 206 atwhich the hub meets the flange. This relief helps reduce transmission ofbending from the hub to the flange which would cause gram load change.

Refer to FIGS. 3a and 3 b which illustrate the base plate of FIG. 2. Anactuator arm 308 and head suspension 300, which are elements of anactuator arm assembly, are connected end to end by the base plate. Thebase plate includes a flat flange portion 200 and a cylindrical hubportion or boss 202. The hub has an inner barrel with an inner diameter204. The inner diameter is perpendicular to the plane of the base plateflange 200. A number of teeth 210, 212, 214, 216, 218, 220, 222, 224,226, 228, protrude from hub.

In assembling a suspension assembly, the hub 202 is inserted through aload beam boss hole in a load beam 300 which is part of the suspensionand the flange portion 200 is welded 302, 304, etc. to the load beam. Tocreate the actuator arm assembly, the hub is force fitted in an actuatorarm boss hole 306 in an actuator arm 308. Pressure is applied to forcethe hub 202 into the boss hole in the actuator arm, rigidly connectingthe hub and attached load beam to the actuator arm boss hole. The hubouter diameter 310 is greater than the nominal diameter of the boss hole306 in the actuator arm 308. To aid the hub in aligning and entering theactuator boss hole 306, a hub outer diameter lead-in chamfer and/or anactuator arm boss hole lead-in chamfer may be provided.

In the embodiment shown ten teeth are illustrated, however, thoseskilled in the art will understand that more or less teeth may beprovided, of the same or differing lengths, extending the full length ofthe hub or part way to the flange/hub intersection and/or part way toouter end of the hub.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand detail may be made therein without departing from the scope of theinvention.

What is claimed is:
 1. A base plate to be press fitted into an actuatorarm boss hole of a predetermined nominal diameter comprising: a flange;and, a hub extending from a region at which said hub meets said flangeto an outer end of said hub; said hub having an outer surface; saidouter surface of said hub having a number of teeth formed on said outersurface and extending axially along at least a portion of said outersurface that engages an inner surface of said actuator arm boss hole,said hub having an outer diameter including said teeth which is greaterthan said predetermined nominal diameter of said actuator arm boss hole.2. The base plate of claim 1 wherein: Said teeth extend from said outerend of said hub to a point that is located between said outer end ofsaid hub and said region at which said hub meets said flange.
 3. Thebase plate of claim 2 wherein: said hub has a corner relief groove thatcircumscribes a region at which said hub meets said flange.
 4. The baseplate of claim 1 wherein: said teeth extend from an outer end of saidhub to a region at which said hub meets said flange.
 5. The base plateof claim 4 wherein: said hub has a corner relief groove thatcircumscribes a region at which said hub meets said flange.
 6. The baseplate of claim 1 wherein: said hub has an outer diameter at said regionat which said hub meets said flange which is not greater than saidpredetermined nominal diameter, and said teeth extend outward to anouter diameter which is greater than said predetermined nominaldiameter.
 7. The base plate of claim 6 wherein: said hub has a cornerrelief groove that circumscribes a region at which said hub meets saidflange.
 8. The base plate of claim 1 wherein: said hub has a cornerrelief groove that circumscribes a region at which said hub meets saidflange.
 9. A base plate to be press fitted into an actuator arm bosshole of a predetermined nominal diameter comprising: a flange; and, ahub contiguous with said flange; said hub having an outer surface; saidhub extending perpendicular to said flange and extending from a regionat which said hub meets said flange to an outer end of said hub; saidhub having a number of teeth protruding radially outwardly from saidouter surface and extending axially along at least a portion of saidouter surface that engages an inner surface of said actuator arm bosshole; said hub having an outer diameter including said teeth which isgreater than said predetermined nominal diameter of said actuator armboss hole; said teeth being arranged along a circumference of said outersurface of said hub such that said teeth occupy less than half saidcircumference.
 10. The base plate of claim 9 wherein: Said teethextending from said outer end of said hub to a point that is locatedbetween said outer end of said hub and said region at which said hubmeets said flange.
 11. The base plate of claim 10 wherein: said hub hasa corner relief groove that circumscribes a region at which said hubmeets said flange.
 12. The base plate of claim 9 wherein: said teethextend from said outer end of said hub to said region at which said hubmeets said flange.
 13. The base plate of claim 12 wherein: said hub hasa corner relief groove that circumscribes said region at which said hubmeets said flange.
 14. The base plate of claim 9 wherein: said hub hasan outer diameter at said region at which said hub meets said flangewhich is not greater than said predetermined nominal diameter, and eachsaid teeth extends outward to a teeth outer diameter which is greaterthan said predetermined nominal diameter.
 15. The base plate of claim 9wherein: said hub has a corner relief groove that circumscribes a regionat which said hub meets said flange.